Inevitably all of us on this forum have our own individual experiences, so all you can do is read them and work out what is possible for your father.
In my case, other than the usual grogginess coming out of anaesthesia, the main problem was pain. I am pretty sure it was "wind" - the rectum, which normally lies just behind the prostate, gets pretty knocked around by the robotic arm. As a result it s very sensitive to being stretched by a "bubble" of wind. But that only lasted a couple of days.
I don't recall any problems with eating. I think when I first came round a nibble on a sandwich was all I wanted, and my grogginess meant drinks with straws or similar involved less effort. However for food, as hinted above, avoid anything that might irritate the bowel, probably best no spicy food.
As described by others, your father will have a catheter until the sewn-up urethra is thought to have sufficiently healed. There may be some quite scary looking clots passed down it, presumably clearing away any bleeding during surgery. Managing a catheter tends to give you a slower pace of life which is no bad thing after an operation, in fact his body will take a while to recover. People tend to forget that a prostatectomy is pretty major surgery even though the incisions may be small, and takes a lot out of the body. Expect your father to want more sleep than usual, possibly for months.
Once the catheter is out, the next problem will be continence, and one thing I have learned from this forum is there has been a wide range of experiences. Some people are continent almost immediately, others improve slowly, and a very few have persistent problems. In most cases continence returns most quickly for the night time. My own personal experience is of initally having days punctuated by frequent pad changes, restricting activities. Slowly those became fewer, though in my case I still need to use a pad over 4 years later (just one a day) whereas others are pad-free.
The other longer term issue is erectile function, not really mentioned yet, and a whole topic of itself. That takes longer to return, assuming the surgeon has been able to preserve the nerves needed. Lots of advice on this forum!